Halogen-free fire retardant system for low heat release polymers

ABSTRACT

An intumescent fire retardant system for making polymeric moldings that is halogen-free and provides fire shielding, thermal shielding and a low heat release rate. The intumescent fire retardant system of the present invention comprises, on the basis of 100 parts by weight blended mixture, 20-45 parts of a polymeric binder based on high density polyethylene and an α-olefin-containing copolymer, such as linear low density polyethylene, and 5-25 parts of a nitrogenous gas-generating agent, 10-30 parts of a water vapor-generating agent, 1-5 parts of an antioxidant, and 0-15 parts of a reinforcing agent. The fire retardant system of the present invention is essentially halogen-free.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.10/771,916 filed on Feb. 4, 2004 and published on Aug. 4, 2005 as U.S.Patent Publication No. 2005/171254, which was filed on even date withU.S. patent application Ser. No. 10/771,972 published as U.S. PatentPublication No. 2005/0170238. The disclosures of the above applicationsare incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to an intumescent flame retardant system formoldable polymeric materials.

2. Description of the Related Art

Intumescent materials contain ingredients that decompose on severeheating to generate gases and form an incombustible or low combustibleresidue. The expelled gases expand the residue to form a foam layer withimproved thermal insulation properties. Materials also having a low heatrelease rate are advantageous in that once they are exposed to fire theyrelease less heat to neighboring materials and diminish firepropagation. This is important because if, for example, a fire isstarted in a warehouse where large quantities of materials are stored,the fire will not get out of control and will be easily extinguishedwhen fire retardant low heat release materials are used in place ofordinary polymers. Hence, major applications for low heat releasepolymers are for shipping pallets and shipping containers. However, suchpolymers can be used wherever there are fire safety concerns. Thepolymers can be used for automotive applications, such as for a fireshield for fuel tanks, car floors, bulk heads, wheel well covers or inother places in cars, trucks, boats, or airplanes to provide resistanceto ignition or resistance to flame travel from the fire source to otherareas. Applications in residential or commercial structures could helpfire containment within each structure as well as slowing down thespread of fire from one structure to a neighboring structure. Hence,fire containment is more easily accomplished when flammable substratesare substituted with low heat release fire retardant polymers.Replacement of metal parts with such polymers, in applications requiringfire integrity, would also lead to appreciable weight reduction.

Shipping pallets will be used as an example to demonstrate theadvantages of using polymers with low heat release rate, though theinvention is not so limited. Pallets are portable platforms used forhandling, storing or moving materials and heavy packages around in awarehouse or during shipping. Pallets have been traditionally made ofwood. More and more plastics are being used to replace wood for thefollowing benefits: (1) plastics maintain consistent weight anddimensions and are easy to stack; (2) plastics will not harbor bacteriaand other contaminants; (3) plastics are easy to handle and clean; (4)plastics do not rot, splinter, or corrode; (5) plastics reducetransportation and disposal costs; (6) plastics are recyclable; (7)plastics perform consistently with automated equipment; (8) plastics aresafe and easy to use; (9) plastics have improved toughness andstiffness; and (10) plastics lend themselves to embedding trackingdevices.

As more plastic is being used in this market to replace wood pallets,fire performance becomes a concern. Plastic pallets are being requiredto meet or exceed the fire resistance standards for wood pallets. Thestandards include requirements that the material should have low heatrelease rate and low flame spread rate. By way of example, polyethylene,which is the preferred material for making pallets, melts, drips andburns at a relatively fast rate when exposed to fire. On the other hand,polyethylene is strong and durable, and has a low cost, high impactresistance and high chemical resistance. Thus, flame retardant systemshave been developed for use with plastics, such as polyethylene, thatattempt to provide intumescence, low heat release rate and low flamespread rate without decreasing the strength, durability, and impact andchemical resistance of the plastic to unacceptable levels. The sameefforts have been made in other markets were flame retardant plasticmaterials are desirable. Invariably, however, some loss in the physicalproperties of the polymeric material is experienced upon addition ofinorganic flame retardant materials to the polymer matrix.

The flame retardant materials must therefore provide a desired balancebetween physical properties, such as impact strength, tensile strength,elongation, and elasticity, and flame retardant properties, such asflame spread control, melt dripping, smoke, peak and average heatrelease rate, and total heat release. By way of example, U.S. Pat. No.5,834,535 entitled “Moldable Intumescent Polyethylene and ChlorinatedPolyethylene Compositions”, and U.S. Pat. No. 6,184,269 entitled“Moldable Intumescent Materials Containing Novel Silicone Elastomers”describe flame retardant plastic systems that address the need forachieving improved resistance to fire in desirable plastics without anunacceptable decrease in physical properties. However, the materialsdescribed therein contain a halogen material, namely, chlorinatedpolyethylene, which may generate corrosive HX gases, such as HCl. Thesetoxic by-products are dangerous to persons exposed thereto. Many similarefforts to develop flame retardant systems utilize halogenatedcomponents because halogens are very efficient fire retardants. However,because they are environmentally unfriendly, it is desirable to find afire retardant system that does not use halogens.

Thus, there is a need to formulate a non-halogen polymeric material thatis strong and durable, that has a low cost, high impact resistance andhigh chemical resistance, that burns at a slow rate, that does not melt,drip and flow, and that releases a relatively low amount of heat whenexposed to fire.

SUMMARY OF THE INVENTION

An intumescent fire retardant system is provided for use in makingpolymeric moldings that is halogen-free and provides fire shielding,thermal shielding and a low heat release rate. The fire retardant systemof the present invention may be blended into many types of thermoplasticand thermoset polymers to produce fire retardant materials with goodphysical properties in addition to good flammability performance. Tothat end, the intumescent fire retardant system of the present inventioncomprises, on the basis of 100 parts by weight blended mixture, 20-45parts of a polymeric binder including an α-olefin-containing copolymer,such as linear low density polyethylene copolymer, and a high densitypolyethylene having a density in the range of 0.940-0.970 g/cm³. Thefire retardant system further comprises 5-25 parts of a nitrogenousgas-generating agent, 10-30 parts of a water vapor-generating agent, 1-5parts of an antioxidant, and 0-15 parts of a reinforcing agent. Notably,the fire retardant system of the present invention is essentiallyhalogen-free.

The nitrogenous gas-generating agent may be an amine, urea, guanidine,guanamine, s-triazine, and/or amino acid, salts thereof, and/or mixturesthereof. The salts are advantageously phosphates, phosphonates,phosphinates, borates, cyanurates, sulfates, and mixtures thereof.Exemplary nitrogenous gas-generating agents include ammonium salt, suchas ammonium phosphates, polyphosphates, pyrophosphates, and cyanurates,and melamine salts, including melamine phosphates, polyphosphates,pyrophosphates and cyanurates. Exemplary water vapor-generating agentsinclude hydrated magnesia, intercalated graphite, hydrated alumina andmixtures thereof. Exemplary antioxidants includedistearylthiodipropionate, hindered phenols, and mixtures thereof.Exemplary reinforcing agents include glass fibers, mica, titanium oxideand mixtures thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of an apparatus for measuring theefficiency of an intumescent fire retardant polymeric composition,according to the present invention; and

FIG. 2 is a graph depicting the peak heat release rate, the average heatrelease rate, and the total heat released for various concentrations ofthe intumescent fire retardant system of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention provides an intumescent fire retardant system thatmay be used by itself or that may be added to a polymeric material toproduce a moldable material with good physical properties that burns ata slow rate, has a low heat release rate, and has intumescence toprovide fire and heat shielding. The fire retardant system does notcontain halogens, and is therefore an environmentally safer system thanfire retardants that rely on halogenated components for theirefficiency. The present invention further provides intumescent fireretardant polymeric compositions that are thermoplastic moldingcompositions that can be blow molded, injection molded, compressionmolded or otherwise suitably molded and shaped to a desired geometry orconfiguration by thermal processes. Polymeric materials produced usingthe fire retardant system of the present invention, and thus having lowheat release rate, are advantageous in that once they are exposed tofire they release less heat to neighboring materials and diminish firepropagation.

In accordance with the present invention, compounds based on nitrogenchemistry (for example melamine cyanurate or ammonium cyanurate) ornitrogen phosphorus chemistry (such as ammonium polyphosphate ormelamine pyrophosphate) can be formulated with other ingredients toproduce intumescent formulations that not only are efficient as fireretardants but also are efficient in reducing the heat release rate,during burning, of polymers to which they are added. These nitrogenousgas-generating agents form 5-25 parts by weight of the fire retardantsystem. A combination of resins is used as a polymeric binder for theintumescent fire retardant ingredients to provide desirable physicalproperties for the fire retardant system and/or for the polymericmaterial to which the system is added. The polymeric binder forms 20-45parts by weight of the fire retardant system. High density polyethylene(HDPE) is used in the binder for its strength, durability, low cost,high impact resistance and high chemical resistance. Anα-olefin-containing copolymer may also be used in the binder for addedimpact strength. In an exemplary embodiment, the fire retardant systemof the present invention includes 20-45 parts by weight of HDPE and 0-15parts by weight of the α-olefin-containing copolymer for a totalpolymeric binder content of 20-45 parts. The fire retardant system ofthe present invention further includes 10-35 parts by weight of one ormore water vapor-generating agents for intumescence, 1-5 parts by weightof an antioxidant for heat stability, and optionally, up to 15 parts byweight of a reinforcing agent. The fire retardant system of the presentinvention may be used by itself as a moldable polymeric material, or itmay be added in any desired amount, for example in an amount of 20-45parts by weight, to a moldable polymeric material to achieve a desiredbalance between physical properties and flammability performance.

The HDPE constituent of the fire retardant system of the presentinvention has a density in the range of 0.940-0.970 g/cm³. Suchmaterials are produced using suitable known catalysts at a relativelylow pressure of ethylene. HDPE assists in preventing melt drippingduring a fire. HDPE is available with molecular weights ranging from alow molecular weight of about 10,000 (usually waxes) to an ultrahighmolecular weight (UHMW-HDPE) of several million. Wide variation ofbranching and density are also available.

Many grades of HDPE may be used in the present invention depending onthe application and the method of processing. High molecular weight/highmelt viscosity grades are used for blow molding applications. Low meltviscosity grades are preferred for injection molding. Extrusion isnormally performed using intermediate melt viscosity. HDPE by itself maybe formulated into the intumescent system, for example, in an amount of20-45 parts by weight of the system formulation; however, the resultingpolymer may have poor mechanical properties, which may be unacceptablefor particular applications. Thus, a portion of the polymer binder, forexample, up to 15 parts by weight of the system formulation, isadvantageously an α-olefin-containing copolymer having a density lessthan the density of the HDPE. For example, the α-olefin-containingcopolymer may be a linear low density polyethylene copolymer having adensity in the range of 0.870-0.910 g/cm³. Exemplary α-olefin-containingcopolymers include copolymers of ethylene with one of butene, hexene andoctene. The ethylene-butene, ethylene-hexene, and ethylene-octenecopolymers advantageously have a density in the range of 0.870-0.910g/cm³. The ethylene-octene copolymers supplied by ExxonMobil ChemicalCo. under the Exact® product line are exemplary, for example, Exact®0210 and Exact® 8210.

The nitrogenous gas-generating agent is present in the fire retardantsystem of the present invention in an amount of 5-25 parts by weight.These agents generate nitrogen-containing gases in order to foam thepolymeric matrix before the material is consumed by the fire. Theresidue that remains after burning most of the organic material willhave a porous char structure and will thus be effective as a thermalbarrier. The nitrogenous gas-generating agents may be any of amines,ureas, guanidines, guanamines, s-triazines, amino acids, salts thereof,and mixtures thereof. These agents emit N₂ gas or NH₃ gas when heated.Advantageously, the nitrogenous gas-generating agent is a salt,including phosphates, phosphonates, phosphinates, borates, cyanurates,sulfates, and mixtures thereof. Further advantageously, the nitrogenousgas-generating agent is one or more of phosphates, polyphosphates,pyrophosphates or cyanurates of ammonium or melamine. Thus, thenitrogenous gas-generating agent may be a nitrogen-containing compoundthat generates N₂ or NH₃ gas upon heating, or a nitrogen andphosphorous-containing compound that generates N₂ or NH₃ gas uponheating. The phosphorous-containing compounds may also form phosphoricacid upon heating, which will act as a catalyst to encourage charformation.

The water vapor-generating agent is present in the fire retardant systemof the present invention in an amount of 5-25 parts by weight. Theseagents induce intumescence and cool down the fire. Hydrated magnesia isparticularly effective, but hydrated alumina will also emit water vaporduring burning. Intercalated graphite has also been found to induceintumescence. Intercalated graphite is produced by treating graphitewith acid and then washing the acid out, leaving behind water betweenthe crystalline layers of the graphite. Upon heating, the water expands,thereby expanding the graphite, and vaporizes to produce water vaporthat cools down the fire. Thus, in an exemplary embodiment of thepresent invention, hydrated magnesia and intercalated graphite are usedin combination to provide intumescence and a low heat release rate.

An antioxidant is included in the fire retardant system of the presentinvention in an amount of 1-5 parts by weight to impart thermal andoxidation stability. Although any suitably compatible stabilizer may beused with HDPE and the α-olefin-containing copolymer for protectionagainst heat and oxygen, it has been found that a system consisting ofdistearylthiodipropionate (DSTDP) and a butylated reaction product ofp-cresol and dicyclopentadiene (e.g., Wingstay®) is very effective as anantioxidant. Other thio-based antioxidants and/or hindered phenolantioxidants may be used for stabilizing the intumescent materialagainst thermal oxidation.

Optionally, the fire retardant system of the present invention mayinclude a reinforcing agent, such as a glass fiber reinforcing filler,which is added in an amount up to 15 parts by weight to provide anincreased strength in the structure of the intumescent material afterburning, and to enhance the action of the system as a fire shield. Thepresence of 3% or higher of glass fiber reinforcing filler may be neededin some formulations to prevent the intumesced residue from beingfriable, which means brittle or easily broken into small fragments orreduced to powder. Advantageously, the fire retardant system includes3-10% glass fibers. In addition to glass fibers, other reinforcingagents may be used to provide strength to the residue, includingtitanium dioxide and mica. A mixture of various reinforcing agents mayalso be used.

None of the constituents of the fire retardant system of the presentinvention includes a halogen. Thus, the fire retardant system of thepresent invention is essentially halogen-free. By essentially, we referto the possibility that small impurity amounts of halogens may bepresent in the raw materials used to form the fire retardant system, butthe total halogen content should be less than 0.5 parts by weight. Mostadvantageously, the fire retardant system will contain 0% halogencontent.

The mixing of compositions described herein on a laboratory scale wasachieved by different methods. The ingredients for each formulation ofthe composition were weighed and dry blended. Melt mixing and extrusioninto a continuous rod was accomplished by using a Brabender extruderwith a 20 mm barrel diameter. The extruder was designed to have three(3) heating zones on the barrel. These heating zones were controlled attemperatures ranging between 150° C. and 290° C. depending on thecomposition of the material being extruded. The rod die was heated to260° C. or lower temperatures. The extruded rod was allowed to come toroom temperature before pelletizing. Pellets were used to compressionmold about 2 mm thick slabs. Samples for UL fire testing, fire shieldingtest, and for mechanical properties were cut from the compression moldedsamples.

Three other methods have been used for melt mixing samples in thelaboratory. The first involved the use of a two roll heated mill. For anintumescent formulation based on polyethylene, the rolls were preheatedto 65° C., and the resins and stabilizers were shear mixed for aboutfive minutes. During this time, the temperature rises to about 150° C.due to shearing. The rest of the ingredients were then added and allowedto mix for an additional period of about five to ten minutes, dependingon the how fast a uniform blend is observed.

The second method for melt blending the compositions was by using aBrabender bowl, which is a small internal mixer. The cavity was heatedto 120° C. before adding the resins and stabilizer. The blades insidethe mixing bowl were rotated at 120 rpm and the ingredients were mixedfor about 2 to 3 minutes. The temperature during this stage of mixingwas not allowed to exceed 140° C. The rest of the ingredients were thenadded in, and thoroughly mixed.

The third method of laboratory mixing employed a 2-pound Banburyinternal mixer. A similar procedure to that used for the Brabender ballmixing was employed. Good mixing leading to a uniform product wasobserved using each of the above mixing procedures.

For all these processes, higher temperatures are used when processingresins with a higher melting point than polyethylene. Uniformity ofmixing is determined by two methods. The amount of filler in the matrixis determined by measuring percent ash remaining after pyrolysis. Aminimum of three samples from each extruded batch are analyzed. Samplesare pyrolyzed in a furnace at 800° C. for 10 minutes; the remaining ashis weighed after cooling to room temperature (see ASTM D 1278), andpercent ash content is calculated. Ash content is a measure of inorganicfiller in the sample that remains after all organics and volatiles aredriven off by pyrolysis. Variation in ash content between batches shouldnot exceed ±3%. Processing conditions used in the lab for proper mixingof the compositions are used to guide large-scale factory mixing of thecompositions.

A Buss Kneader extruder with a 70 mm or larger diameter barrel followedby a single screw extruder has been successfully used to produce similarformulations. All ingredients except the reinforcing agent are dry mixedtogether, placed in a super sack and poured into a hopper. The dry mixis fed from the hopper to the Buss Kneader extruder using a gravimetricfeeder to meter in the material at the exact desired rate. The extruderbarrel is heated to temperatures ranging from 140-180° C. In the barrel,the polymeric binder melts and the mixing process with the otheringredients begins. Mixing continues as the material travels down theheated barrel. In the Buss Kneader, mixing is performed using a lowshear screw. The reinforcing agent, such as glass fibers, is introducedat a later stage using a port closer to the extruder exit in order topreserve the glass fiber from excessive breakage. The polymer melt thenexits the Buss Kneader and enters a crosshead single screw extruder tocomplete the blending process. The blended mixture is then extruded intoribbons by exiting through a multi-strand ribbon die. The ribbons arethen cut at the die face into pellets using a rotating knife. Thepellets are dropped onto a bed and cooled using air or water before theyare dried and conveyed to a container for storage and shipping.

Flammability testing and mechanical properties determination wereconducted on samples prepared in the lab. The main function of theintumescent fire retardant polymeric composition is in resisting thespread of flame from a fire source and shielding articles protected bythe composition from high temperature rise. The characteristics orproperty of intumescence efficiency may be measured by a procedure usingan apparatus as described in connection with FIG. 1 or by the ASTM E1354cone calorimeter method.

All of the compositions illustrated in this specification have beentested to assess the fire shielding capabilities of the intumescent fireretardant polymeric compositions, according to the present invention.The standardized test for evaluating and/or verifying fire performanceis the ASTM E1354 cone calorimeter test. Another relatively simple testfor evaluating fire-shielding capabilities involves exposing plaquesmade of the intumescent fire retardant polymeric compositions, accordingto the present invention, to a Bunsen flame for long periods of time.This small scale “Bunsen-burner” test is effective for productdevelopment in the laboratory setting. In the “Bunsen-burner” test,flame temperatures are in excess of 1000° C. The sample is considered topass this test if it continues to provide fire shielding for at leastthirty (30) minutes without burn through, or melt dripping. Because theshielding is not compromised, a drastic reduction in temperature on thesurface of the sample opposite to the flame is achieved.

A “Bunsen-burner” test apparatus 10 is schematically shown in FIG. 1.The apparatus 10 includes a three-wall steel chamber comprising leftside wall 12, back wall 14, and right side wall 16. Each wall is a steelplate 229 mm high, 127 mm wide, and 1 mm thick. The walls are joined attheir edges as illustrated in FIG. 1 to form a generally square-shaped(in cross-section) chamber with an open side or front.

A 152 mm by 152 mm by 1 mm thick steel plate adapted to be placed on topof the walls 12, 14, and 16 is employed as a roof member 18. During atest, the roof member 18 carries affixed to its lower surface a molded127 mm by 152 mm by 2.75 mm rectangular molded slab 20 of material to betested for intumescence effectiveness as a heat shield. It should beappreciated that the thickness of 2.75 mm of the test specimen (as wellas its composition) is important to the repeatability of this test. Asillustrated, the slab 20 faces downward inside of the roof member 18 andchamber during the test. On the top surface 22 of the roof member 18 arelocated six thermocouple leads in the locations indicated, respectively101, 102, 103, 104, 105, and 106. It should be appreciated that testspecimens with other thickness values can also be tested.

A 165 mm tall Bunsen burner 24 is used as the flame or fire source. Theheight of the burner 24 does not include the flame height. The flameheight on top of the burner 24 is on the order of 60 mm, and it isadjusted during each test so that the tip of the inner blue cone of theflame 25, its hottest part, touches the surface of the intumescentmaterial test specimen. A thermocouple indicated at 26 was placed at thelower surface of the slab 20 to measure the flame temperature as itimpinged on the intumescent material at that point. The flametemperature as measured by the thermocouple 26 was at a location on theintumescent material opposite the location of the thermocouple 104 onthe top surface 22 of the roof member 18.

While six thermocouple locations are indicated in FIG. 1, experience hasshown that equivalent useful data is obtained from using only fourthermocouples at locations 101, 102, 104, and 106. It should beappreciated that temperature differences between the flame thermocoupleand the roof plate thermocouples are used as a measure of theeffectiveness of intumescent material in providing thermal and fireshielding.

Aspects of the present invention will now be illustrated, withoutintending any limitation, by the following examples. Unless otherwiseindicated, all parts and percentages are by weight.

EXAMPLES

Table 1 lists a general formulation of a concentrate or fire retardantsystem of the present invention that may be used alone or may be addedto different polymers to make intumescent fire retardant polymers. Thecomponents and the amounts of each component have been further describedin detail above. Table 1 also lists four exemplary formulations 1-4 inaccordance with the present invention.

In Formulation 1, the non-halogen fire retardant additive is an ammoniumpolyphosphate (FR CroS™ 484, Budenheim). A combination of resins is usedas the polymer binder for the intumescent fire retardant ingredients.The first resin is an injection molding grade of HDPE (T50-2000, BPSolvay Polyethylene) having a density of 0.953 g/cm³ (ASTM D4883) and amelt index of 20 g/10 min. at 190° C. under a load of 2.16 kg (ASTMD1238). The second resin used is a linear low density ethylene-α-olefincopolymer (Exact® 0210, ExxonMobil Chemical Co.) that has a density of0.902 g/cm³, and a melt index of 25 g/10 min. Specifically, Exact® 0210is an ethylene octene copolymer produced by ExxonMobil using ametallocine single site catalyst. The resin is added to the formulationto improve impact strength.

The hydrated magnesia (Magshield®) and intercalated graphite both emitwater vapor at high temperatures, and are added to intumesce thematerial and to slow down heat release from the polymer material duringfire. The antioxidants DSTDP (distearylthiodipropionate) and Wingstay® L(a hindered amine) are added to impart heat stability and improve theaging characteristics of the material.

The above concentrate or system may be added to other polymers atvarious concentrations to build up a desired degree of fire retardancyfor the polymeric material. For example, when the fire retardantformulation is added to an injection molding grade of HDPE (e.g.,T50-2000, from BP Solvay) at 30 wt. % level, it imparts fire retardancyby slowing down the horizontal burn rate and preventing flaming meltdripping of the resin, and gives rise to an appreciably decreased amountof heat release when the material is on fire.

The mechanical properties of the fire retardant polymer composition madeby mixing 30 wt. % of Formulation 1 with 70 wt. % injection moldinggrade HDPE (T50-2000) are shown in Table 2. The mechanical properties,although lower than those of the original resin, are still good. Thenotched Izod impact strength is 0.63 ft-lb/inch, which is close to the0.77 ft-lb/inch value measured for the virgin HDPE resin without theflame retardant system.

The fire retardant polymer made with Formulation 1 burns slowly, doesnot drip during burning, and hence does not spread fire to neighboringmaterials. It also generates a low amount of smoke. When the formulationwas flame tested using the ASTM E1354 cone calorimeter method, under aheat flux of 35 kW/m², the peak heat release rate (intumescenceefficiency) was 414 kW/m², as shown in FIG. 2, as compared to 917 kW/m²for virgin HDPE. The amount of smoke generated during fire was 15 m²(total smoke) as compared to 8 m² for virgin polyethylene and much lessthan the 40 to 82 m² normally measured for fire retardant polymers.

The fire retardant intumescent Formulation 2, also shown in Table 1, wasdeveloped based on melamine cyanurate (BUDIT® 315). Formulation 2 alsoproduces polymers with reduced peak heat release rate. Formulation 2used a blow molding grade of HDPE in a greater amount than the injectionmolding grade HDPE in Formulation 1 (30 and 13 parts, respectively). Adifferent grade of linear low density ethylene octene copolymer wasused, namely Exact® 8210, in a lesser amount than the grade used inFormulation 1 (13 and 30 parts, respectively). This copolymer is alsomade by ExxonMobil using the metallocene single site catalyst. Thecopolymer has elastic and plastic properties, and when added to theintumescent formulation, it enhances impact resistance of the material.The copolymer has a density of 0.882 g/cm³ and a melt index of 10 g/10min. measured per ASTM D1238.

When 30 wt. % of Formulation 2 is added to 70 wt. % of an injectionmolding grade of HDPE (T50-2000 from BP Solvay), good mechanicalproperties are obtained as seen in Table 2 above. The notched Izodimpact strength is 0.66 ft-lb/in. The burning characteristics are alsogood. The horizontal burn test measured per UL 94-HB was only 17 mm/min.Only a slight degree of melt dripping and very low concentration ofsmoke were observed during fire. The results from the ASTM E1354 conecalorimeter test conducted at 35 kW/m² are also good. It took 117seconds to ignite the sample compared to 102 seconds for virginpolyethylene. However, the biggest improvement was for the peak heatrelease rate, which was measured at 372 kW/m² (shown in FIG. 2) ascompared to 917 kW/m² for the virgin HDPE. Smoke generation was only 15m² (total smoke) compared to values of 40 to 82 m² measured for otherfire retardant polymers.

Formulations 3 and 4 set forth in Table 1 can also be added to HDPE orother polymers to reduce the heat release rate, as shown in FIG. 2. Thetwo formulations were made using identical materials, including a blowmolding grade of HDPE, except that Formulation 3 includes 22 partshydrated magnesia as the sole water vapor-generating agent andFormulation 4 includes a combination of 19.8 parts hydrated magnesia and10 parts intercalated graphite as the water vapor-generating agent, withthe amounts of the other components in the formulation being decreasedto accommodate the graphite addition. Addition of either of these fireretardant systems into HDPE appreciably reduces the peak heat releaserate from 917 kW/m² for polyethylene by itself to the values shown inFIG. 2. The heat release rate decreases with increase in theconcentration of either formulation in the HDPE. However, the presenceof intercalated graphite in Formulation 4 leads to a more prominentdecrease in the peak and average rates of heat released. The total heatrelease rate is essentially the heat of combustion and is essentiallythe same with and without graphite.

While physical properties are described for a 30 wt. % concentration ofthe fire retardant system of the present invention in HDPE, it should beunderstood that fire retardant systems of the present invention, such asFormulations 1-4, may be combined with various polymeric materials andat various ratios to prepare intumescent fire retardant polymerscompositions. For example, the fire retardant system of the presentinvention may be added in an amount of 20-45 wt. % to a polymericmaterial to provide a balance between physical properties andflammability properties. In addition to polyethylene, the fire retardantsystem of the present invention may also be added to otherthermoplastics such as polypropylene, nylon, polystyrene,styrene-acrylonitrile copolymers, and butadiene-styrene-acrylonitrileterpolymers, or to thermoset polymers such as polyurethanes and epoxies,in order to make non-halogen fire retardant polymeric materials that, ina fire, will intumesce to provide better heat shielding and slow heatrelease rate. Advantageously, a fire retardant polymeric composition ofthe present invention has a peak heat release rate of less than 500kW/m², as measured by the ASTM E1354 cone calorimeter test, and moreadvantageously, less than 400 kW/m².

Polymer compositions made using the fire retardant system of the presentinvention can be employed in a variety of applications to provide firesafety, including applications for the shipping and warehousingindustry, automotive and other transportation industries, and othercommercial and residential applications.

While the present invention has been illustrated by the description ofone or more embodiments thereof, and while the embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus and methodand illustrative examples shown and described. Accordingly, departuresmay be made from such details without departing from the scope or spiritof the general inventive concept.

1. An intumescent fire retardant system for use in polymeric moldings,comprising, on the basis of 100 parts by weight blended mixture of apolymer component comprising: 20-45 parts of a polymeric bindercomprising high density polyethylene having a density in the range of0.940-0.970 g/cm³ and an α-olefin-containing copolymer in the range of0.870-0.910 g/cm³, wherein the system comprises 20-45 parts of the highdensity polyethylene and 0-15 parts of the α-olefin-containing copolymerfor a total of 20-45 parts polymeric binder; 5-25 parts of a nitrogenousgas-generating agent selected from the group consisting of amines,ureas, guanidines, guanamines, s-triazines, amino acids, salts thereof,and mixtures thereof, wherein the salts are selected from the groupconsisting of phosphates, phosphonates, phosphinates, borates,cyanurates, sulfates and mixtures thereof; 10-35 parts of a watervapor-generating agent; 1-5 parts of an antioxidant; and 0-15 parts of areinforcing agent, wherein the system is essentially halogen-free. 2.The fire retardant system of claim 1 wherein the α-olefin-containingcopolymer is a copolymer of ethylene with one of butene, hexene andoctene.
 3. The fire retardant system of claim 1 wherein theα-olefin-containing copolymer is a linear low density ethylene octenecopolymer.
 4. The fire retardant system of claim 1 wherein nitrogenousgas-generating agent is an ammonium salt, a melamine salt, or a mixturethereof.
 5. The fire retardant system of claim 1 wherein the nitrogenousgas-generating agent is selected from the group consisting of: melaminephosphates, melamine polyphosphates, melamine pyrophosphates, melaminecyanurates, ammonium phosphates, ammonium polyphosphates, ammoniumpyrophosphates, ammonium cyanurates, and mixtures thereof.
 6. The fireretardant system of claim 1 wherein the water vapor-generating agent isselected from the group consisting of: hydrated magnesia, hydratedalumina, intercalated graphite, and mixtures thereof.
 7. The fireretardant system of claim 1 wherein the antioxidant is selected from thegroup consisting of: distearylthiodipropionate, a hindered phenol, andmixtures thereof.
 8. The fire retardant system of claim 1 wherein thereinforcing agent is selected from the group consisting of: glassfibers, mica, titanium oxide and mixtures thereof.
 9. An intumescentfire retardant polymeric moldable composition comprising, on the basisof 100 parts by weight blended mixture: 55-80 parts of a polymericmatrix; and 20-45 parts of the intumescent fire retardant system ofclaim
 1. 10. The intumescent fire retardant polymeric composition ofclaim 9 wherein the polymeric matrix is a thermoplastic polymer selectedfrom the group consisting of: polypropylene, nylon, polystyrene, astyrene-acrylonitrile copolymer, and a butadiene-styrene-acrylonitrileterpolymer.
 11. The intumescent fire retardant polymeric composition ofclaim 9 wherein the polymeric matrix is a thermoset polymer selectedfrom the group consisting of a polyurethane and an epoxy.
 12. Theintumescent fire retardant polymeric composition of claim 9 wherein thepolymeric matrix is a thermoplastic polymer selected from the groupconsisting of: injection molding grade high density polyethylene, blowmolding grade high density polyethylene, and extrusion molding gradehigh density polyethylene.
 13. An intumescent fire retardant system foruse in polymeric moldings, comprising, on the basis of 100 parts byweight blended mixture: 20-45 parts of a polymeric binder comprisinghigh density polyethylene having a density in the range of 0.940-0.970g/cm³ and an α-olefin-containing copolymer having a density in the rangeof 0.870-0.910 g/cm³, wherein 20-45 parts of the blended mixture is thehigh density polyethylene and 0-15 parts of the blended mixture is theα-olefin-containing copolymer; 15-25 parts of a nitrogenousgas-generating agent selected from the group consisting of an ammoniumsalt, a melamine salt, or mixtures thereof, wherein the salts areselected from the group consisting of phosphates, phosphonates,phosphinates, borates, cyanurates, sulfates and mixtures thereof; 20-30parts of a water vapor-generating agent selected from the groupconsisting of hydrated magnesia, hydrated alumina, intercalatedgraphite, and mixtures thereof; 1-5 parts of an antioxidant selectedfrom the group consisting of distearylthiodipropionate, a hinderedphenol, and mixtures thereof; and 3-10 parts of a reinforcing agentselected from the group consisting of glass fibers, mica, titanium oxideand mixtures thereof, wherein the system is essentially halogen-free.14. The fire retardant system of claim 13 wherein theα-olefin-containing copolymer is a copolymer of ethylene with one ofbutene, hexene and octene.
 15. The fire retardant system of claim 13wherein the α-olefin-containing copolymer is a linear low densityethylene octene copolymer.
 16. The intumescent fire retardant polymericcomposition of claim 13 wherein the polymeric matrix is a thermoplasticpolymer selected from the group consisting of: polypropylene, nylon,polystyrene, a styrene-acrylonitrile copolymer, and abutadiene-styrene-acrylonitrile terpolymer.
 17. The intumescent fireretardant polymeric composition of claim 13 wherein the polymeric matrixis a thermoset polymer selected from the group consisting of apolyurethane and an epoxy.
 18. The intumescent fire retardant polymericcomposition of claim 13 wherein the polymeric matrix is a thermoplasticpolymer selected from the group consisting of: injection molding gradehigh density polyethylene, blow molding grade high density polyethylene,and extrusion molding grade high density polyethylene.
 19. Anintumescent fire retardant thermoplastic moldable compositioncomprising, on the basis of 100 parts by weight blended mixture: 55-80parts of a thermoplastic matrix; and 20-45 parts of an intumescent fireretardant additive comprising on the basis of 100 parts by weightblended mixture: 20-45 parts of a polymeric binder comprising highdensity polyethylene having a density in the range of 0.940-0.970 g/cm³and an α-olefin-containing copolymer having a density less than thedensity of the high density polyethylene; 5-25 parts of a nitrogenousgas-generating agent selected from the group consisting of amines,ureas, guanidines, guanamines, s-triazines, amino acids, salts thereof,and mixtures thereof, wherein the salts are selected from the groupconsisting of phosphates, phosphonates, phosphinates, borates,cyanurates, sulfates, and mixtures thereof; 10-35 parts of a watervapor-generating agent; 1-5 parts of an antioxidant; and 0-15 parts of areinforcing agent, wherein the thermoplastic polymer matrix and theintumescent fire retardant additive are each essentially halogen-free,and wherein the composition exhibits a peak heat release rate of lessthan 500 kW/m² as measured by the ASTM E1354 cone calorimeter method.